Interaction of ethylbenzene and styrene with iron oxide model catalyst films at low coverages: A NEXAFS study

Abstract

The adsorption of ethylbenzene and styrene on well ordered epitaxial iron oxide model catalyst films with different stoichiometries was investigated using near edge X-ray absorption fine structure spectroscopy (NEXAFS). On the iron-terminated Fe3O4(111) and α-Fe2O3(0001) surfaces a chemisorption of ethylbenzene and styrene is observed whi ch initially occurs on the iron sites via the π-electron system of the phenyl ring. This forces the molecules into an almost flat lying configuration (η 6 like ring adsorption geometry). In the case of ethylbenzene this adsorption complex is supposed to lead to an activation of the C-H bonds thus facilitating the dehydrogenation to styrene. The tilt angle of the aromatic ring systems increase to about 40° when approaching monolayer saturation. In contrast, the interaction with the oxygen-terminated FeO(111) surface is weak and of the physisorption type. The adsorbate-adsorbate interaction dominates and causes a tilted adsorption of the molecules from the beginning.

Surface chemistry and catalysis on well-defined epitaxial iron-oxide layers

“…6.23 does not allow us to separate the intensities at normal incidence into contributions from the phenyl and vinyl groups. From [358].…”

“…Styrene adsorption has been studied by NEXAFS on the three Fe-oxide films [333,358]. The condensed phase spectrum of St is contained in Fig.…”

Styrene synthesis: in situ characterization and reactivity studies of unpromoted and potassium-promoted iron oxide model catalysts

“…Based on the observations that both the right adsorption strength and -at least on unpromoted Fe 2 O 3 -defects are necessary for high conversion, a model for the catalytic cycle has been proposed [32]. The adsorbate-substrate bond via the π-system of the benzene ring is responsible for holding the molecules long enough on the surface.…”

Epitaxial iron oxide growth on a stepped Pt(9 11 11) surface

“…The controlled introduction of defects into oxide surfaces may be useful for the identification of reactive surface sites in heterogeneous catalysis. A mechanism that involves defects has been suggested for the catalytic dehydrogenation of ethylbenzene to styrene on iron oxides [3,4]. Due to their lower coordination or modified bond structure, step and kink atoms may be more reactive in gas adsorption and catalysis as also was found in first experiments on metals [5].…”

“…Both Fe 3 O 4 and Fe 2 O 3 are catalytically active with the latter being most active. It has been proposed that defects on Fe 2 O 3 play an essential role [3,4]. In an attempt to prepare well-defined defects, we investigate here if atomic steps can be prepared in a controlled way by growing iron oxide films on a stepped Pt(9 11 11) substrate.…”